Dual focal length lens system

ABSTRACT

A dual focal length optical system includes a first optical system and a second optical system. The first optical system is positioned along an optical path and includes an optical structure having an object side surface and an image side surface. The first optical system also includes a first surface of an intermediate reflective element located between the object side surface and the image side surface of the optical structure as viewed along the optical path. The first optical system has a first focal length. The second optical system shares a portion of the same optical path and includes a second surface of the same intermediate reflective element as that of the first optical system. The second optical system has a second focal length. The first focal length of the first optical system is longer than the second focal length of the second optical system.

FIELD OF THE INVENTION

This invention relates generally to the field of reflective opticalsystems, and in particular to optical systems suitable for use incompact imaging systems.

BACKGROUND OF THE INVENTION

Optical systems that combine reflective optics with refractive opticsare known. For example, U.S. Pat. No. 7,049,597, issued to Bodkin, andU.S. Pat. No. 7,119,969, issued to Amon, disclose a dual optical pathwith reflective and refractive elements for use in a dual spectrumoptical system. Each optical system includes one optical system forvisible imaging and another optical system for hyperspectral imaging. Abeam splitter is used to form two optical paths.

U.S. Pat. No. 5,051,830, issued to Von Hoessle, discloses a refractivelens with inner and outer zones is disclosed. Light from the outer zonetravels to a reflective lens which focuses the light onto a firstsensor. Light from the inner zone is focused onto a second sensor thatis located in a back to back configuration with the first sensor. Asingle electronic system is used to support both imaging systems so thatonly one of the imaging systems can be used at a time. The positioningof the two sensors is designed to minimize weight in a guided missileapplication. The shorter focal length imaging system is provided forgeneral guidance of the missile to the target. The longer focal lengthimaging system is provided for more accurate guidance of the missileduring the final stage of guidance of the missile to the target.

U.S. Pat. No. 6,870,690, issued to Lawson, discloses a lens in which anouter portion of the lens is designed for one spectral band and an innerportion of the lens is designed for another spectral band. U.S. Pat. No.5,172,235, issued to Wilm, discloses two lenses that are focused ontoone sensor. Complimentary zone filters enable the two images from thetwo lenses to overlay one another to produce a composite image withdifferent areas of resolution.

There is still a need, however, to provide a compact imaging systemincorporating a dual focal length lens system that includes twoindependent lens systems that simultaneously provide different focallength images of the same scene or object.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a dual focal length opticalsystem includes a first optical system and a second optical system. Thefirst optical system is positioned along an optical axis and includes anoptical structure having an object side surface and an image sidesurface. The object side surface and the image side surface include arefractive surface portion and a reflective surface portion. The firstoptical system has a focal length. The second optical system ispositioned on the same optical axis and has a focal length. The focallength of the first optical system is longer than the focal length ofthe second optical system.

According to another aspect of the invention, a dual focal lengthoptical system includes a first optical system and a second opticalsystem. The first optical system is positioned along an optical path andincludes an optical structure having an object side surface and an imageside surface. The first optical system also includes a first surface ofan intermediate reflective element located between the object sidesurface and the image side surface of the optical structure as viewedalong the optical path. The first optical system has a first focallength. The second optical system shares a portion of the same opticalpath and includes a second surface of the same intermediate reflectiveelement as that of the first optical system. The second optical systemhas a second focal length. The first focal length of the first opticalsystem is longer than the second focal length of the second opticalsystem.

BRIEF DESCRIPTION OF THE DRAWINGS

In the detailed description of the preferred embodiments of theinvention presented below, reference is made to the accompanyingdrawings, in which:

FIG. 1 is a schematic diagram showing a ray trace of light propagatingthrough a first example embodiment of the invention;

FIG. 2 is a schematic diagram of the optical components of the firstexample embodiment of the invention;

FIG. 3 is a schematic drawing showing an example implementation of thefirst example embodiment of the invention;

FIG. 4 is a schematic drawing showing a ray trace of light propagatingthrough a second example embodiment of the invention;

FIG. 5 is a schematic drawing showing a ray trace of light propagatingthrough a portion of the second example embodiment of the inventionshown in FIG. 4;

FIG. 6 is a schematic drawing showing a ray trace of the lightpropagating through a portion of the second example embodiment of theinvention shown in FIG. 4; and

FIG. 7 is a schematic drawing showing an example implementation of thesecond example embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present description will be directed in particular to elementsforming part of, or cooperating more directly with, apparatus inaccordance with the present invention. It is to be understood thatelements not specifically shown or described may take various forms wellknown to those skilled in the art.

Referring to FIG. 1, a schematic drawing showing a ray trace of lightpropagating through a first embodiment of a dual focal length lenssystem 100 is shown. Dual focal length lens systems 100 includes a first(for example, a telephoto) optical system 200 and a second (for example,a wide angle) optical system 300. The optical surfaces (described inmore detail with reference to FIG. 2) of first optical system 200 definea catadioptric optical system in which optical system 200 includes bothrefractive and reflective optical surfaces having optical power. Theoptical surfaces (described in more detail with reference to FIG. 2) ofsecond optical system 300 define a dioptric optical system in whichoptical system 300 includes refractive optical surfaces having opticalpower.

First optical system 200 and second optical system 300 are positionedalong an optical axis 125 and share optical surfaces of an opticalelement(s). Surfaces 105 and 110 define a lens element 140 having weakrefracting optical power, commonly referred to as a corrector plate,that is used for both first optical system 200 and second optical system300. Different portions of lens element 140 are used for each lenssystem with first optical system 200 using an outer annular region 115and second optical system 300 using a central region 120.

Surface 105 of lens element 140 is aspheric and surface 110 of lenselement 140 is spherical. However, either or both surfaces 105 and 110can be aspheric to help correct aberrations. Alternatively, surfaces 105and 110 can be plano to act as a cover window to protect the remainingoptical system from contamination.

First optical system 200, having a focal length, is positioned along anoptical path or optical axis 125. Second optical system 300, having afocal length, is positioned along the same optical path 125. The focallength (a first focal length) of first optical system 200 is longer thanthe focal length (a second focal length) of second optical system 300.First optical system 200 directs light to an image sensor 130 whilesecond optical system 300 directs light to an image sensor 135.

Referring to FIG. 2, first optical system 200 includes an opticalstructure 205 having an object side surface 210 and an image sidesurface 215. Object side surface 210 includes a refractive surfaceportion 220 and a reflective surface portion 225. Image side surface 215includes a refractive surface portion 230 and a reflective surfaceportion 235.

Reflective surface portion 235 of image side surface 215 of opticalstructure 205 has optical power and is aspheric. Reflective surfaceportion 225 of object side surface 210 of optical structure 205 also hasoptical power and is spherical. However, reflective surface portion 225can be aspheric. The majority of the optical power for first opticalsystem 200 is present in reflective surface 235 and 225. As surfaces 235and 225 are reflective these surfaces do not introduce chromaticaberration into optical system 200. First optical system 200 includes anaperture 290.

The space between surfaces 225 and 235 can be filled with air or arefractive material (described in more detail with reference to FIG. 3).When this space is filled with a refractive material, the dispersion ofthe material may introduce some chromatic aberration. When this happens,a refractive optical element 240 having surfaces 245 and 250 positionedbetween image sensor 130 and optical structure 205 can be used tocorrect chromatic aberration as well as field aberration if fieldaberration is present.

As shown in FIG. 2, refractive surface portion 230 of image side surface215 of optical structure 205 includes one or both of surfaces 245 and250 of optical element 240. However, when the space between surfaces 225and 235 is filled with a refractive material (see FIG. 3), refractivesurface portion 230 of image side surface 215 of optical structure 205can be formed, for example, by molding a radius of curvature, from thematerial itself.

As shown in FIG. 2, refractive surface portion 220 of object sidesurface 210 of optical structure 205 includes one or both surfaces 105and 110 of lens element 140. Accordingly, the optical power of objectside surface 210 of optical structure 205 is less than the optical powerof image side surface 215 of optical structure 205. Alternatively,object side surface 210 of optical structure 205 can include anothersurface(s). For example, when lens element 140 is a plano plate, objectside surface 210 can be a surface of another lens element or an objectside surface 330 of the material used to fill the space between surfaces225 and 235 (see FIG. 3).

Still referring to FIG. 2 and back to FIG. 1, different portions of lenselement 140 are used for each lens system with first optical system 200using an outer annular region 115 and second optical system 300 using acentral region 120. In this sense, object side surface 210 of opticalstructure 205 includes a first refractive surface portion 115 and asecond refractive surface portion 120 with the second refractive surfaceportion 120 being associated with second optical system 300 and thefirst refractive surface portion 115 being associated with the firstoptical system 200. As shown in FIGS. 1 and 2, the first refractivesurface portion 115 and the second refractive surface portion 120 ofobject side surface 210 of optical structure 205 form a continuoussurface but this does not always have to be the case. Additionally, thefirst refractive surface portion 115 and the second refractive surfaceportion 120 of object side surface 210 of optical structure 205 have thesame radius of curvature. However, refractive surface portions 115 and120 can have different radii of curvature.

Table 1A describes one specific configuration of first lens system 200of the first example embodiment of the invention. In this configuration,lens system 200 is a telephoto lens system. However, it is recognizedthat other configurations are permitted. Typically, these otherconfigurations depend on the specific application contemplated for firstlens system 200 of dual focal length lens system 100.

TABLE 1A Surface Surface Number Type Radius of Curvature ThicknessMaterial 105 Asphere 57.8494675050496 1 531200.560000 110 Sphere59.625042170115 14 235 Asphere −20.2112695127046 —6.797583 225 Sphere−10.0720729924657 7.703927 245 Sphere −4.07618390798256 0.5531200.560000 250 Sphere −155.495425161355 1.7 ASPHERIC  CONSTANTS$Z = {\frac{({CURV})Y^{2}}{1 + \left( {1 - {\left( {1 + K} \right)({CURV})^{2}Y^{2}}} \right)^{1/2}} + {(A)Y^{4}} + {(B)Y^{6}} + {(C)Y^{8}} + {(D)Y^{10}}}$ASPHERIC CURV K A A(1) 0.01728624 0.0 −4.19841E−05 A(3) −0.049477350.261217 0.00E+00 ASPHERIC B C D A(1) −5.13601E−07 1.09172E−08−1.21494E−10 A(3) 0.00E+00 0.00E+00 0.00E+00

Still referring to FIG. 2, second optical system 300 shares surfaces 105and 110 of optical element 140 with first optical system 200. Afterpassing through optical elements 140, second optical system 300 directslight to image sensor 135 through one or more additional lenses 255. Asshown in FIG. 2, these lenses include a biconvex lens having surfaces260, 265; a biconvex lens having surfaces 270, 275; and a biconcave lenshaving surfaces 280, 285. Alternatively, second optical system 300 canhave more or less lenses than the number of lenses shown in FIG. 2.

The majority, if not all, of the optical power for optical system 300 iscontained in surfaces 260 through 285. Lenses 255 form a three elementlens group having a +, +, − optical power, but other configurations arejust as viable. Surfaces 260 through 285 are spherical, however, any ofthese optical surfaces can have aspheres for aberration control.

Table 1B describes one specific configuration of second lens system 300of the first example embodiment of the invention. In this configuration,lens system 300 is a wide angle lens system. However, it is recognizedthat other configurations are permitted. Typically, these otherconfigurations depend on the specific application contemplated for firstlens system 300 of dual focal length lens system 100.

TABLE 1B Surface Surface Number Type Radius of Curvature ThicknessMaterial 105 Asphere 57.8494675050496 1 531200.560000 110 Sphere59.625042170115 1.00000 260 Sphere 7.60261 1.00000 Schott NFK5 265Sphere −4.49456 1.00000 270 Sphere 3.12733 1.00000 Schott NFK5 275Sphere −7.67950 1.00000 280 Sphere −3.10732 0.75000 Schott SF6 285Sphere 4.59180 0.61382 ASPHERIC  CONSTANTS$Z = {\frac{({CURV})Y^{2}}{1 + \left( {1 - {\left( {1 + K} \right)({CURV})^{2}Y^{2}}} \right)^{1/2}} + {(A)Y^{4}} + {(B)Y^{6}} + {(C)Y^{8}} + {(D)Y^{10}}}$ASPHERIC CURV K A A(1) 0.01728624 0.0 −4.19841E−05 ASPHERIC B C D A(1)−5.13601E−07 1.09172E−08 −1.21494E−10

Referring back to FIGS. 1 and 2, at least one of the first focal lengthof first optical system 200 and the second focal length of secondoptical system 300 is a fixed focal length. However, it is contemplatedthat an additional optical element(s) can be positioned between eitheror both of the image sensor 130 and first optical system 200 and imagesensor 135 and second optical system 300 that is moveable in order toaffect a change in focal length, focus, or both. This can beaccomplished using conventional techniques for moving one or moreoptical elements. Alternatively, one or both of image sensor 130 andimage sensor 135 can be moveable along its associated optical path toaffect a change in focus. Movement of the image sensor(s) isaccomplished using conventional techniques. In another alternativeembodiment, first optical system 200 or second optical system 300 can bemoved relative to their respective image sensors 130 and 135 to affect achange in focus. Again, movement is accomplished using conventionaltechniques.

A controller can be provided and configured to perform a digital zoomingfunction using both the images produced by first optical system 200 andsecond optical system 300 of dual focal length lens system 100. Digitalzooming can be accomplished using techniques like the one described inU.S. patent application Ser. No. 11/461,574 filed Aug. 1, 2006 Border etal, the disclosure of which is incorporated by reference herein.

Referring to FIG. 3 and back to FIG. 2, an example implementation 360 ofdual focal length lens system 100 is shown. Optical structure 205 is asolid material element that includes two pieces 310, 320 cementedtogether around lenses 255 and image sensor 135. Suitable materialsinclude low dispersion materials like acrylic plastics, cyclo olefinpolymers (cop), for example, Zeonex, which is commercially availablefrom the Zeon Corporation, Tokyo, Japan. Piece 310 includes element 140which serves as refractive surface portion 220 of object side surface210. Piece 320 includes reflective surface portion 225 of object sidesurface 210 and reflective surface portion 235 of image side surface215. In FIG. 3, the material surface in the middle of reflective surfaceportion 235 of image side surface 215 is plano, so refractive opticalelement 240 serves as the refractive surface portion 230 of image sidesurface 215. Example implementation 360 of dual focal length lens system100 also includes a light blocking surface 350 on piece 320 that formsaperture 290. In FIG. 3, optical elements 255 are the same as thoseoptical lenses described with reference to FIG. 2. Image sensor 130 isalso shown.

Referring to FIG. 4, a schematic drawing showing a ray trace of lightpropagating through a second embodiment of a dual focal length lenssystem 400 is shown. Dual focal length lens system 400 includes a first(for example, a telephoto) optical system 500 and a second (for example,a wide angle) optical system 600. The optical surfaces (described inmore detail with reference to FIG. 5) of first optical system 500 definea catadioptric optical system in which optical system 500 includes bothrefractive and reflective optical surfaces having optical power. Theoptical surfaces (described in more detail with reference to FIG. 6) ofsecond optical system 600 define a dioptric optical system in whichoptical system 600 includes refractive optical surfaces having opticalpower. First optical system 500 and second optical system 600 share aportion of an optical axis 410, some optical surfaces and opticalelements.

First optical system 500, having a first focal length, is positionedalong an optical path or optical axis. Second optical system 600, havinga second focal length, shares a portion of the same optical path. Theoptical path is depicted using the ray trace of light propagatingthrough optical system 400. The first focal length of first opticalsystem 500 is longer than the second focal length of second opticalsystem 600.

Referring to FIG. 5, first optical system 500 includes an opticalstructure 550 that includes an object side surface 505 and an image sidesurface 510 as viewed along the optical path (depicted by the ray traceof light propagating through optical system 500). An intermediateoptical element 515 is located between object side surface 505 and imageside surface 510 of optical structure 550. First optical system 500 alsoincludes a first surface 520 of intermediate element 515.

Object side surface 505 has some positive optical power which helps toreduce the overall length of first optical system 500. Object sidesurface 505 is aspheric, however, surface 505 can also be spherical.Image side surface 510 is a reflective surface that provides a greateramount of optical power (when compared to surface 505) and does sowithout adding chromatic aberration because it is reflective. Image sidesurface 510 can also be aspheric. Surface 520 of intermediate element515 is a plano reflecting surface, for example, a mirror surface, withno optical power that redirects or folds the optical path or axis offirst optical system 500.

As shown in FIG. 5, first optical system 500 includes a secondintermediate optical element with intermediate optical element 515 beinga first intermediate optical element. Intermediate element includesrefractive surface 525 and is positioned along a portion of the opticalpath that is not shared by second optical system 600. Surface 525 isincluded in optical structure 550. However, optical surface 525 can be asurface of an intermediate optical element that is not part of opticalstructure 550. First optical system 500 directs light to an image sensor530. Although not shown in FIG. 5, an additional optical element(s) canbe positioned between image sensor 530 and first optical system 500 likethe optical elements positioned between image sensor 675 and secondoptical system 600 (described with reference to FIG. 6). In FIG. 5,surface 525 is plano. However, surface 525 can have optical power andoptionally be aspheric in order to be used as a field correctionsurface, a way to control lateral color, or both.

Table 2A describes one specific configuration of first lens system 500of the second example embodiment of the invention. In thisconfiguration, lens system 500 is a telephoto lens system. However, itis recognized that other configurations are permitted. Typically, theseother configurations depend on the specific application contemplated forfirst lens system 500 of dual focal length lens system 400.

TABLE 2A Surface Surface Radius of Number Type Curvature ThicknessMaterial 505 Asphere  28 17 531200.560000 510 Sphere −65 −11531200.560000 520(515) Sphere le+018 8 531200.560000 525 Sphere le+0181.62803743654473 ASPHERIC  CONSTANTS$Z = {\frac{({CURV})Y^{2}}{1 + \left( {1 - {\left( {1 + K} \right)({CURV})^{2}Y^{2}}} \right)^{1/2}} + {(A)Y^{4}} + {(B)Y^{6}} + {(C)Y^{8}} + {(D)Y^{10}}}$ASPHERIC CURV K A A(1) 0.03571429 0.261217 0.0E+00 ASPHERIC B C D A(1)0.0E+00 0.0E+00 0.0E+00

Referring to FIG. 6, second optical system 600 shares surface 505 withfirst optical system 500. Second optical system 600 includes a secondsurface 620 of intermediate element 515. In this instance, secondsurface 620 is opposite first surface 520. Second surface 620 ofintermediate element 515 is a plano reflecting surface with no opticalpower that redirects the optical path or axis of second optical system600.

When designing dual focal length lens system 400, second surface 620 canbe designated as the aperture stop of second optical system 600 in orderto reduce or minimize the physical space requirements of surface 620(and intermediate element 515). Similarly, first surface 520 onintermediate element 515 can be designated as the aperture stop of firstoptical system 500.

Second optical system 600 includes optical surface 625 which isspherical and has optical power. Surface 625 can be aspheric. Opticalsurface 625 is included in optical structure 550. In this sense, opticalsurface 625 is a second image side surface of optical structure 550 withimage side surface 510 of optical structure 550 being a first image sidesurface of optical structure 550. However, it should noted that opticalsurface 625 is refractive whereas image side surface 510 is reflective.Optical surface 625 is positioned along a portion of the optical paththat is not shared by first optical system 500. Alternatively, opticalsurface 625 can be a surface of an optical element that is not part ofoptical structure 550.

After passing through optical surface 625, second optical system 600directs light to an image sensor 675 through one or more additionallenses. As shown in FIG. 6, these lenses include a doublet havingsurfaces 630, 635, 640; a biconvex lens having surfaces 645, 650; andfirst and second meniscus lenses having surfaces 655, 660 and 665,670,respectively. First and second meniscus lenses are both concave on theirimage sensor 675 side. Alternatively, second optical system 600 can havemore or less lenses than the number of lenses shown in FIG. 6.

Table 2B describes one specific configuration of second lens system 600of the second example embodiment of the invention. In thisconfiguration, lens system 600 is a wide angle lens system. However, itis recognized that other configurations are permitted. Typically, theseother configurations depend on the specific application contemplated forfirst lens system 600 of dual focal length lens system 400.

TABLE 2B Surface Surface Number Type Radius of Curvature ThicknessMaterial 505 Asphere 28 6 531200.560000 620(515) Sphere le+018 −8531200.560000 625 Sphere 15.7235349193283 −0.1 630 Sphere−72.4903253521872 −0.320000000000003 728300.283000 635 Sphere−6.348244432915 −3.23214999780346 620400.603000 640 Sphere7.1739813793011 −0.0999999999999989 645 Sphere −11.2953941892583−1.89457378858138 568700.631000 650 Sphere 15.4906964613072−0.0999999999999999 655 Sphere −4.07305249656168 −1.65033497854948692300.547000 660 Sphere −8.68370524690205 −0.555762452403168 665 Sphere−73.1325877974812 −0.32 728300.283000 670 Sphere −10.4032594561083−0.42066077910744 ASPHERIC  CONSTANTS$Z = {\frac{({CURV})Y^{2}}{1 + \left( {1 - {\left( {1 + K} \right)({CURV})^{2}Y^{2}}} \right)^{1/2}} + {(A)Y^{4}} + {(B)Y^{6}} + {(C)Y^{8}} + {(D)Y^{10}}}$ASPHERIC CURV K A B C D A(1) 0.03571429 0.261217 0.0E+00 0.0E+00 0.0E+000.0E+00

Referring back to FIGS. 4-6, at least one of the first focal length offirst optical system 500 and the second focal length of second opticalsystem 600 is a fixed focal length. However, it is contemplated that anadditional optical element(s) can be positioned between either or bothof the image sensor 530 and first optical system 500 and image sensor675 and second optical system 600 that is moveable in order to affect achange in focal length, focus, or both. This can be accomplished usingconventional techniques for moving one or more optical elements.Alternatively, one or both of image sensor 530 and second image sensor675 can be moveable along its associated optical path to affect a changein focus. Movement of the image sensor(s) is accomplished usingconventional techniques. In another alternative embodiment, firstoptical system 500 or second optical system 600 can be moved relative totheir respective image sensors 530 and 675 to affect a change in focus.Again, movement is accomplished using conventional techniques.

A controller can be provided and configured to perform a digital zoomingfunction using both the images produced by first optical system 500 andsecond optical system 600 of dual focal length lens system 400. Digitalzooming can be accomplished us techniques like the one described in U.S.patent application Ser. No. 11/461,574 filed Aug. 1, 2006, Border etal., the disclosure of which is incorporated by reference herein.

Referring to FIG. 7 and back to FIGS. 5 and 6, an example implementation700 of dual focal length lens system 400 is shown. Optical structure 550is a solid material element that includes two pieces 710, 720 cementedtogether around intermediate optical element 515. Suitable materialsinclude low dispersion materials like acrylic plastics, cyclo olefinpolymers (cop), for example, Zeonex, which is commercially availablefrom the Zeon Corporation, Tokyo, Japan. Intermediate element 515 (andreflective surface 520), surface 525, and the object side surface 505and the image side surface 510 of optical structure 550 of first opticalsystem 500 make up portions of the same optical element. Additionally,this optical element also includes reflective surface 620 ofintermediate element 515 and surface 625 of second optical system 600.In FIG. 7, optical elements 730 are the same as those optical lensesdescribed with reference to FIG. 6. Image sensors 530 and 675 are alsoshown.

Optical systems that use reflective and refractive optics to createoptical systems including two separate imaging systems sharing a commonoptical axis can be used in many applications. By sharing a commonoptical axis, the two separate imaging systems can be made to provideimages without parallax differences. Optical systems like thosedescribed above are particularly well suited for compact imagingsystems. The reflective optics essentially fold the optical system ontoitself, thereby reducing the overall length of the optical system.Configuring the optical system to share at least a portion of a commonoptical axis also reduces physical space requirements and decreases thecomplexity of the optical system when compared to optical systems thatdo not share a common optical axis.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the scope of theinvention.

PARTS LIST

-   -   100 dual focal length lens system    -   105 refractive surface    -   110 refractive surface    -   115 outer annular region (first refractive surface portion)    -   120 central region (second refractive surface portion)    -   125 optical axis or path    -   130 image sensor    -   135 image sensor    -   140 refractive element    -   200 first optical system    -   205 optical structure    -   210 object side surface    -   215 image side surface    -   220 refractive surface portion    -   225 reflective surface portion    -   230 refractive surface portion    -   235 reflective surface portion    -   240 refractive optical element    -   245 refractive surface    -   250 refractive surface    -   255 lenses    -   260 refractive surface    -   265 refractive surface    -   270 refractive surface    -   275 refractive surface    -   280 refractive surface    -   285 refractive surface    -   290 aperture    -   300 second optical system    -   310 piece    -   320 piece    -   330 object side surface    -   350 light blocking surface    -   360 optical system implementation    -   400 dual focal length lens system    -   410 optical axis    -   500 first optical system    -   505 object side surface    -   510 image side surface    -   515 intermediate optical element    -   520 first reflective surface    -   525 refractive surface    -   530 image sensor    -   550 optical structure    -   600 second optical system    -   620 second reflective surface    -   625 refractive surface    -   630 refractive surface    -   635 refractive surface    -   640 refractive surface    -   645 refractive surface    -   650 refractive surface    -   655 refractive surface    -   660 refractive surface    -   665 refractive surface    -   670 refractive surface    -   675 image sensor    -   700 implementation    -   710 piece    -   720 piece    -   730 optical elements

1. A dual focal length optical system comprising: a first optical systempositioned along an optical path, the first optical system including anoptical structure having an object side surface and an image sidesurface, the first optical system also including a first reflectivesurface of an intermediate reflective element located between the objectside surface and the image side surface of the optical structure asviewed along the optical path, the first optical system having a firstfocal length; and a second optical system sharing a portion of the sameoptical path and including a second reflective surface of the sameintermediate reflective element as that of the first optical system, thesecond optical system having a second focal length, the first focallength of the first optical system being longer than the second focallength of the second optical system.
 2. A dual focal length opticalsystem comprising: a first optical system positioned along an opticalpath, the first optical system including an optical structure having anobject side surface and an image side surface, the first optical systemalso including a first surface of an intermediate reflective elementlocated between the object side surface and the image side surface ofthe optical structure as viewed along the optical path, the firstoptical system having a first focal length; a second optical systemsharing a portion of the same optical path and including a secondsurface of the same intermediate reflective element as that of the firstoptical system, the second optical system having a second focal length,the first focal length of the first optical system being longer than thesecond focal length of the second optical system; and a secondintermediate element associated with the first optical system, thesecond intermediate element including an optical surface positionedalong a portion of the optical path that is not shared by the secondoptical system.
 3. The system of claim 2, wherein the secondintermediate element includes an aspheric surface.
 4. The system ofclaim 2, wherein the first intermediate element, the second intermediateelement, and the object side surface and the image side surface of theoptical structure of the first optical system make up portions of thesame optical element.
 5. The system of claim 4, wherein the opticalelement is a solid material element.
 6. The system of claim 5, whereinthe solid material element comprises two elements cemented together. 7.The system of claim 4, the image side surface of the optical structureof the first optical system being a first image side surface of theoptical structure, the second optical system including the object sidesurface of the optical structure and a second surface of the opticalstructure that is not shared by the first optical system.
 8. The systemof claim 1, the image side surface of the optical structure of the firstoptical system being a first image side surface of the opticalstructure, the second optical system including the object side surfaceof the optical structure and a second surface of the optical structurethat is not shared by the first optical system.
 9. A dual focal lengthoptical system comprising: a first optical system postioned along anoptical path, the first optical system including an optical structurehaving an object side surface and an image side surface, the firstoptical system also including a first surface of an intermediatereflective element located between the object side surface and the imageside surface of the optical structure as viewed along the optical path,the first optical system having a first focal length; and a secondoptical system sharing a portion of the same optical path and includinga second surface of the same intermediate reflective element as that ofthe first optical system, the second optical system having a secondfocal length, the first focal length of the first optical system beinglonger than the second focal length of the second optical system;wherein the image side surface of the optical structure of the firstoptical system being a first image side surface of the opticalstructure, the second optical system including the object side surfaceof the optical structure and a second surface of the optical structurethat is not shared by the first optical system; and wherein the secondsurface of the optical structure includes optical power.
 10. The systemof claim 9, wherein the second surface of the optical structure includesan aspheric surface.
 11. The system of claim 1, wherein the object sidesurface of the optical structure includes an aspheric surface.
 12. Thesystem of claim 1, wherein the image side surface of the opticalstructure includes optical power.
 13. The system of claim 1, wherein theimage side surface of the optical structure includes an asphericsurface.
 14. A dual focal length optical system comprising: a firstoptical system positioned along an optical path, the first opticalsystem including an optical structure having an object side surface andan image side surface, the first optical system also including a firstsurface of an intermediate reflective element located between the objectside surface and the image side surface of the optical structure asviewed along the optical path, the first optical system having a firstfocal length: a second optical system sharing a portion of the sameoptical path and including a second surface of the same intermediatereflective element as that of the first optical system, the secondoptical system having a second focal length, the first focal length ofthe first optical system being longer than the second focal length ofthe second optical system; a first image sensor associated with thefirst optical system; and a second image sensor associated with thesecond optical system.
 15. The system of claim 14, further comprising:an additional optical element positioned between either or both of thefirst image sensor and the first optical system and the second imagesensor and the second optical system.
 16. The system of claim 15,wherein the additional optical element is moveably positioned in orderto affect a change in focal length, focus, or both.
 17. The system ofclaim 14, wherein one or both of the first image sensor and the secondimage sensor is moveable along its associated optical path to affect achange in focus.
 18. The system of claim 14, further comprising: acontroller configured to perform a digital zooming function using boththe images produced by the first optical system and the second opticalsystem.
 19. The system of claim 14, wherein at least one of the firstfocal length of the first optical system and the second focal length ofthe second optical system is a fixed focal length.
 20. The system asclaimed in claim 1, wherein the intermediate Reflective element is fixedin position.